Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 160501
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1101 PM MDT FRI AUG 15 2014

.SHORT TERM...TONIGHT THROUGH SATURDAY

ONE LAST ROUND OF CONVECTION FOR MOST AREAS THIS
EVENING...ESPECIALLY IN NORTHWEST WY...WHERE SOUTHWEST DIFLUENT FLOW
WRAPPING AROUND THE VERTICALLY STACKED H7-H3 PAC NW LOW ENCOURAGES
LIFT BEFORE MUCH LOWER DEW POINTS STREAM IN FROM THE SOUTHWEST LATER
THIS EVE. THEN FORECAST ISSUES SWITCH TO FIRE WEATHER CONCERNS FOR
SATURDAY. WITH MIN RH EXPECTED TO HOVER IN THE LOW TEENS ACROSS
SWEETWATER COUNTY SATURDAY AFTERNOON ALONG WITH INCREASING 15 TO 30
MPH WESTERLY WINDS AS THE GRADIENT TIGHTENS SFC AND ALOFT IN
RESPONSE TO THE PAC NW LOW SCOOTING EAST ALONG THE CANADIAN
BORDER...A FIRE WEATHER WATCH IS IN ORDER FOR FIRE WEATHER ZONE 279
FROM 18Z SATURDAY THROUGH 02Z SUNDAY. HOWEVER...THE NW MTNS
INCLUDING YNP SHOULD SEE ANOTHER ROUND OF AFTERNOON CONVECTION
SATURDAY AS THIS AREA WILL BE UNDERNEATH A JET COUPLET ROUNDING THE
BASE OF THE TROUGH. ANY OTHER CELLS THAT FORM SHOULD BE PRIMARILY BE
MONTANA BORDER HUGGERS. ANY CONVECTIVE CELLS SHOULD BE FAIRLY FAST
MOVERS. TEMPS SHOULD BE RELATIVELY UNCHANGED FOP SATURDAY FOR HIGH
TEMPS.

.LONG TERM...SATURDAY NIGHT THROUGH FRIDAY

THE WAVE MOVING THROUGH NORTHERN MONTANA WILL FLATTEN THE FLOW
OVER THE FORECAST AREA FOR SATURDAY NIGHT. ZONAL FLOW WILL THEN BE
FOUND OVER THE FORECAST AREA THROUGH SUNDAY MORNING. AS THE WAVE
MOVES FURTHER EAST...THERE WILL BE BUILDING NORTHWEST FLOW OVER
THE FORECAST AREA WITH A TRANSITORY RIDGE OF HIGH PRESSURE.
SHOWERS AND THUNDERSTORMS WILL BE ISOLATED TO WIDELY SCATTERED IN
COVERAGE THROUGH TUESDAY. BEYOND THIS...MODELS BEGIN TO FALL OUT
OF SIGNIFICANT AGREEMENT.

ANOTHER APPROACHING AREA OF LOW PRESSURE MAY BRING INCREASED
SOUTHWEST FLOW OVER THE FORECAST AREA BY TUESDAY NIGHT. SOME
INCREASED MOISTURE OVER THE AREA MAY BE PRESENT ON WEDNESDAY
AFTERNOON WITH AN INITIAL WAVE OF LOW PRESSURE. THE ECMWF IS MORE
AGGRESSIVE WITH THIS WAVE...DEMONSTRATING A GREATER POTENTIAL FOR
SHOWER AND THUNDERSTORM ACTIVITY. HOWEVER...MODELS DO VARY ON THE
INTENSITY AND COVERAGE OF THIS ACTIVITY...WITH THE GFS NOT
INDICATING THIS FIRST TROUGH.

BOTH MODELS DO AGREE WITH THE POTENTIAL FOR DEEPENING SOUTHWEST
FLOW BY THURSDAY AND FRIDAY. THE GFS INDICATES A GREATER AREA OF
PRECIPITATION ACROSS NORTHERN WYOMING SINCE IT IS MORE AGGRESSIVE
WITH THE SYSTEMS PATH THROUGH THE FORECAST AREA. BUT...BOTH
MODELS DO SHOW THE POTENTIAL FOR SOME ACTIVITY. THE ECMWF SHOWS
THE DEEPER PUSH OF THE LOW ON FRIDAY EVENING...WITH MORE
WIDESPREAD SHOWER AND THUNDERSTORMS. THE GFS...HAVING ALREADY
PUSHED THE SYSTEM THROUGH THE AREA...SHOWS A WEAKER SOUTHWEST
FLOW...WITH MINIMAL MOISTURE. THE SCENARIOS WILL CONTINUE TO BE
MONITORED AND WILL BE ADJUSTED MORE AS MODELS COME INTO BETTER
AGREEMENT.

&&

.AVIATION.../06Z ISSUANCE/

CONVECTION HAS ENDED WITH SKC TO SCT120 EXPECTED OVERNIGHT...WITH A
VERY QUIET AVIATION THROUGH THE TAF PERIOD. SKC CONDITIONS SATURDAY
MORNING...WITH SOME HIGH BASED CUMULUS DEVELOPING SATURDAY
AFTERNOON...WITH A LIGHT TO BREEZY WEST TO NORTHWEST WIND IN MOST
PLACES. THE ONLY EXCEPTIONS COULD BE SOME VERY LOCALIZED
FOG...MAINLY OUT WEST BETWEEN 09Z AND 15Z...BUT NOT ENOUGH
CONFIDENCE TO EVEN INSERT VCFG AT ANY TERMINAL. ALSO VERY ISOLATED
CONVECTION COULD OCCUR OVER THE FAR NORTH SATURDAY AFTERNOON.

&&

.FIRE WEATHER...

FIRE WEATHER CONCERNS WILL BEGIN TO INCREASE SATURDAY AND SUNDAY AS
THE REGION BEGINS TO GET CUT OFF FROM THE MONSOON MOISTURE AND DRY
WEST TO SOUTHWEST FLOW FILLS IN ACROSS THE REGION. THIS EVENING...A
RELATIVELY WEAK UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE WEST
AND NORTH...COMBINING WITH RESIDUAL MOISTURE AMD DIURNAL FORCING
FROM TERRAIN FEATURES TO GET ISOLATED TO WIDELY SCATTERED CHANCES
FOR THUNDERSTORMS...MAINLY ACROSS THE WESTERN AND NORTHERN
MOUNTAINS WITH WINDS AT OR BELOW 20 MPH EVERYWHERE. THIS
WEEKEND...DRY WESTERLIES REALLY TAKE HOLD WITH LITTLE CHANCE FOR
PRECIPITATION ANYWHERE...EXCEPT FOR THE NORTHWEST MOUNTAINS AND
ALONG THE MONTANA BORDER SATURDAY AFTERNOON...AND LOW ELEVATION
TEMPERATURES RISING INTO THE UPPER 80S TO AROUND 90 WHILE MINIMUM
RH VALUES FALL INTO TH LOWER AND MIDDLE TEENS. WINDS ON SATURDAY
WILL ALSO PICK UP OUT OF THE WEST...WITH GUSTS RANGING TO NEAR
CRITICAL LEVELS...DEFINITELY ENHANCING FIRE DANGER...ESPECIALLY ON
SATURDAY. IN FACT A FIRE WEATHER WATCH HAS BEEN ISSUED FOR FIRE
WEATHER ZONE 279 FROM 1200 THROUGH 2000 SATURDAY AFTERNOON AND
EVENING.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...LIPSON
LONG TERM...BRANHAM
AVIATION...WM
FIRE WEATHER...LIPSON









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